Every pond liner’s primary job is to hold your pond’s water. However, manufacturers make flexible liners — often called “geomembranes” by engineers — with a wide variety of materials, each of which has pros and cons depending on a pond’s individual setup. Your liner needs to stay stable in the hottest and coldest temperatures your area is likely to experience, and it shouldn’t snag, puncture, or tear due to objects or irregularities in the ground underneath. If your liner is exposed, it has to stand up to both UV rays and harsh weather.
Chemical resistance, flexibility, cost, and toxicity to fish can all vary as well. Many geomembrane liners are designed for large lakes or landfills, and as a result they may not perform as well in smaller backyard ponds. For these reasons, it pays to know a little about different liner materials before you invest in one.
How Are Pond Liners Made & Installed?
Pond liners are large, foldable sheets made of either plastic or synthetic rubber. Depending on the material, some companies can custom manufacture liners for individual ponds in-factory. In other cases, you’ll have to hire professionals to form a complete pond liner by joining multiple sheets in the field using methods like welding or taping. A liner material’s pliability, weight, and thickness all influence how difficult it is to install and what you can do with it.
The material you choose should balance these traits in the way that works best for your pond. Your liner should be flexible enough to mold to conform to the contours of your pond, but not liable to stretch to the point of deformity. Thicker liners may last longer in general, but thicker doesn’t always mean stronger. And a liner’s UV and ozone resistance may determine whether you need to cover it or can leave it exposed.
Detailed Pond Liner Material Comparison (Advantages & Disadvantages)
1) HDPE (high density polyethylene)
If you’re looking to line a large pond or lake, you’ll want to consider models made with high density polyethylene (HDPE) plastic. HDPE has very good UV resistance and functions well in cold temperatures. It’s also strong and very stiff, meaning that it’s not prone to sudden length-wise tears. HDPE’s most desirable characteristic, though, might be its superior resistance to a wide range of chemicals. This combined with its relatively inexpensive price (an average of $0.62/square foot in the US, according to HomeAdvisor) and the fact that multiple sheets can be joined using welding have historically made HDPE one of the most popular geomembrane types worldwide. HDPE liners are commonly used in landfills and chemical containment sites, but they are also safe and well-suited for fish ponds. No matter where they are, HDPE liners are very durable, having been found to last upwards of 36 years when covered.
Unfortunately, HDPE liners are far from perfect. Because they’re stiff and fairly heavy, HDPE liners can be expensive to ship and can’t be custom shaped or assembled in a factory. Instead, you’ll have to pay extra installation costs to have them installed on-site by professionals. These expenses make HDPE liners most cost-effective for larger ponds.
HDPE’s lack of flexibility can also make installation more difficult in general, and at extremely high temperatures it can expand and become loose. You’ll have to be careful when installing an HDPE geomembrane on rough terrain, since the material is vulnerable to punctures, and surface scratches that can become cracks over time. In fact, some research suggests that a tendency toward stress cracking, which is caused by low-grade pressure applied over long periods, is HDPE’s greatest weakness.
2) LLDPE (low density polyethylene)
Given that they’re made from the same plastic, it’s no surprise that linear low density polyethylene (LLDPE) and HDPE liners have several things in common. These liner types share the same fairly inexpensive price, and both have to be seamed from multiple sheets in the field by professionals, rather than custom-fabricated in the factory. Like HDPE, LLDPE is weldable, nontoxic to fish, and functions well in in typical pondwater temperatures, though it’s also commonly used in liners that are intended to contain water contaminated with waste or hazardous chemicals.
LLDPE has one major advantage over HDPE, though. Because LLDPE liners aren’t as dense as their HDPE cousins, they’re softer, more flexible, and more pliable. This makes LLDPE liners much easier to install, as well as to mold around corners and tight nooks and crannies. LLDPE’s pliability also means that liners made from it can conform more closely to rough terrain than HDPE liners can, with fewer wrinkles. Because it’s softer, LLDPE is also somewhat less prone to stress cracking than HDPE.
Unfortunately, this softness comes at a price. LLDPE liners have less tensile strength than HDPE liners, meaning they’re more susceptible to length-wise deformation and tears. Geomembranes made from LLDPE are also not quite as resistant to UV rays, chemicals, and oxidation as those made from HDPE. Consequently, LLDPE liners may not be as durable when exposed to the elements (when used as recommended, LLDPE liners may last up to 36 years).
3) RPE (reinforced polyethylene)
Reinforced polyethylene (RPE) provides almost all of the same benefits as HDPE and LLDPE without many of their flaws. Because RPE is reinforced, it’s much one of the most durable liner materials you can buy; it’s certainly stronger and more puncture resistant than either LLDPE or HDPE, even though all three are made from the same plastic. RPE liners are also much thinner than HDPE, LLDPE, and liners from other materials like PVC and EPDM. Add in the fact that RPE liners can weigh up to two-thirds less than other geomembranes, and it’s easy to see why they’re easier and less expensive to ship and install in larger pieces.
Like HDPE and LLDPE liners, RPE geomembranes are weldable, fish safe, and fairly resistant to chemicals and UV rays. RPE liners are stiffer than materials like LLDPE, but they should still fold adequately around most corners in your pond. Outside of the pond industry, you’re most likely to find RPE lining waterbodies like canals and dams.
The only real downside to RPE liners is that they’re more expensive than their HDPE and LLDPE counterparts (an average of $0.84/square foot in the US, according to HomeAdvisor). This makes sense considering that RPE liners require more effort to make and are generally of higher quality than HDPE or LLDPE liners. It’s also worth noting that, because RPE liners are fairly new to the market, there’s little research about their expected lifespan. Some companies claim their RPE products can last up to 40 years when covered, but warranties beyond 20 years are rare. When exposed to sun and weather, RPE liners may last 3–5 years. More time is needed to determine if they have similar lifespans to their LLDPE and HDPE cousins.
4) fPP (flexible polypropylene)
If your pond liner priorities are physical strength and plasticity, then flexible polypropylene (fPP) is definitely worth considering. As the name suggests, fPP liners are very innately flexible without the need for additives like plasticizers. As a result, they can be easily molded and formed to fit your pond’s tightest corners and recesses. fPP geomembranes can also conform tightly to even extremely irregular surfaces, giving them good gripping power against pond slopes and rough terrain. Liners made from fPP can take a lot of strain from different angles and stretch without breaking or deforming, making them fairly resistant to tears, scratches, and punctures. They even remain pliable until -50°C, making them more than suitable for ponds in temperate climates.
fPP liners are heat-treatable and can be seamed through welding. They don’t expand as much in heat as HDPE or LLDPE liners do, though. This means that fPP geomembranes have a wider range of temperatures over which they can successfully welded, making them easier to seam. Also, unlike HDPE and LLDPE liners, fPP liners can be custom-assembled in large pieces and folded up in the factory, which can be advantageous when you’re looking to line a uniquely shaped pond. fPP products are fish safe, moderately priced, and have a lifespan of up to 30 years when covered.
Although fPP liners are resistant to UV rays and many chemicals, there are a few substances that they fall short against. They’re particularly vulnerable to a class of chemicals called hydrocarbons (which includes substances like benzene), as well as chlorine-containing chemicals, oils (including animal fats), and strong oxidants. When exposed to this last type of chemical, fPP liners may develop oxidative damage, including stress cracking along folds and wrinkles. This likely won’t be a problem in most garden fish ponds, but it’s worth keeping in mind if you’re interested in using fPP for a larger application. Outside the pond industry, fPP geomembranes are commonly used to line canals, containers for drinking water and horticulture, and earthen dams.
5) PVC (polyvinyl chloride)
Many people associate polyvinyl chloride (PVC) with pipes and plumbing, but it’s also one of the oldest and most popular pond liner materials. Two of PVC’s biggest selling points are its very low price (an average of $0.65/square foot in the US, according to HomeAdvisor) and its exceptional flexibility. Like fPP geomembranes, PVC liners can conform snugly to tight corners and crevices, and can be fit tightly over coarse surfaces with little difficulty. Additionally, they can be seamed and folded as needed without risking stress cracking. These traits make PVC liners among the easiest to work with and install — an especially big plus if you’re planning to install your liner yourself.
PVC liners also have great chemical resistance and are moderately strong against tears and punctures. Sheets of PVC are weldable but can also be joined using adhesives like liner tape or glue. Most PVC seaming and assembling can be done in the factory of the company you buy from, but some on-field seaming may be necessary depending on the size of the sheets you order.
Unfortunately, PVC liners have a few big shortcomings. For one, PVC liners frequently aren’t fish safe. PVC isn’t naturally flexible, and the plasticizers and other additives included to it to make it that way are often toxic and prone to leach into pondwater. If you’re interested in using a PVC liner in a fish pond, you’ll need to look for varieties that are specifically formulated to be safe for aquatic life. PVC liners also have inferior ozone and UV resistance, and, as a result, they could experience premature degradation unless they’re buried under at least 12″ of sediment (when covered, PVC geomembranes can last between 18 and 32 years, depending on the plasticizers used). This can be a hassle, especially for owners of smaller ponds.
Finally, PVC liners don’t function well at very high or low temperatures; in particularly cold climates, they may be susceptible to cracks and splits. These flaws don’t necessarily mean that you shouldn’t consider a PVC liner for your fish pond, but it would probably be a good idea to weigh them against the material’s low cost and ease of installation.
6) EPDM (Ethylene propylene diene monomer)
Ethylene propylene diene monomer rubber, or EPDM, is a synthetic rubber and one of the most popular geomembrane materials used for lining ponds. EPDM liners are soft but durable, giving them a nice balance of flexibility and toughness. This allows them to stretch without losing strength, conform tightly around curves and corners, and lay flat against a pond’s bottoms and sides. Compared to other liner materials, EPDM doesn’t expand or contract much at high and low temperatures, meaning that extreme temperature differences won’t cause it to lose its close grip on a rough surface. Liners made of this material are especially resilient against the cold and are at little risk of cracking at low temperatures. Despite its softness, EPDM is also moderately puncture resistant and has good endurance against UV rays, ozone, and weathering. EPDM liners’ strength gives them a lifespan of 27 years or more when covered, and they’re nontoxic to fish.
Before you jump to buy a roll of EPDM, though, consider the material’s few drawbacks. EPDM is thermoset, which means that although liners made from it perform well at high and low temperatures, they can’t be welded without losing quality. To seam pieces of EPDM liner together, you (or the professionals you hire) will have to use adhesives like tape. EPDM liners also have poor overall chemical resistance and are particularly vulnerable to degradation from oils and solvents, although this likely won’t be a problem for a typical garden pond.
What could be an issue for anyone, though, is that EPDM geomembranes are relatively heavy, which could result in high shipping fees. And at an average price of $0.84/square foot in the US, according to HomeAdvisor, EPDM liners are already comparatively expensive. EPDM liners are still extremely well-suited for custom fish ponds both large and small, but you should be sure you can account for these issues before you make your purchase.
Butyl (synthetic) rubber has been one of the most widely used pond liner materials in the UK for decades. Like its synthetic rubber sibling EPDM, butyl is highly flexible and easy to mold to the tight spaces in a custom pond. Butyl liners are also very durable, as they are resilient to UV radiation, ozone, and weathering. This perhaps lends credence to the many manufacturers who claim their butyl rubber products have lifespans of up to 50 years, presumably covered (if that seems dubious to you, consider that warranties beyond 20 years are rare). Butyl geomembranes are also similar to EPDM liners in that they are nontoxic to fish and function well in both very high and low temperatures.
Unfortunately, another property that butyl shares with EPDM is its inability to be heat-treated without permanent deformation. This means that butyl liner sheets can’t be welded together; instead, seaming them is difficult and requires the use of liner glue or tape. Butyl also shares EPDM’s inferior chemical resistance. Unfortunately, butyl lacks the high strength that helps EPDM compensate for these shortcomings. Physically, butyl liners are quite weak, making them easy to rip and puncture. This is definitely worth keeping in mind if you’re looking to line a pond covered in rough substrate or which you expect to keep animals with sharper claws, like turtles. At the very least, you’ll have to invest in a strong, high-quality underlay to support a butyl liner.
In the US, butyl liners are fairly cheap (they cost an average of $0.50/square foot in the US, according to HomeAdvisor). In the UK, though, butyl rubber is becoming less common as the cost of the raw materials required to make it increase. As a result, UK prices can be as much as $2.87/square foot, and many UK manufacturers now only supply butyl liners for custom projects. Depending on where you live, butyl pond liner sheets can now be quite expensive, if they’re even available.
No liner material is perfect, but all of the varieties listed here have advantages that could make them valuable additions to a variety of fish ponds, water gardens, and lakes. When you’re comparing liner materials from different manufacturers, though, remember that they’ll more than likely downplay those materials’ flaws, emphasizing only the benefits. Hopefully, this guide will help you shop smart and allow you to more accurately choose the correct liner material for your individual needs and circumstances!